[PATCH V4 00/27] ublk: add UBLK_F_BATCH_IO

Ming Lei
2025-11-21T01:59:08Z

Hello,

This patchset adds UBLK_F_BATCH_IO feature for communicating between kernel and ublk
server in batching way:

- Per-queue vs Per-I/O: Commands operate on queues rather than individual I/Os

- Batch processing: Multiple I/Os are handled in single operation

- Multishot commands: Use io_uring multishot for reducing submission overhead

- Flexible task assignment: Any task can handle any I/O (no per-I/O daemons)

- Better load balancing: Tasks can adjust their workload dynamically

- help for future optimizations:
- blk-mq batch tags free
- support io-poll
- per-task batch for avoiding per-io lock
- fetch command priority

- simplify command cancel process with per-queue lock

selftest are provided.

Performance test result(IOPS) on V3:

- page copy

tools/testing/selftests/ublk//kublk add -t null -q 16 [-b]

- zero copy(--auto_zc)
tools/testing/selftests/ublk//kublk add -t null -q 16 --auto_zc [-b]

- IO test
taskset -c 0-31 fio/t/io_uring -p0 -n $JOBS -r 30 /dev/ublkb0

1) 16 jobs IO
- page copy: 37.77M vs. 42.40M(BATCH_IO), +12%
- zero copy(--auto_zc): 42.83M vs. 44.43M(BATCH_IO), +3.7%

2) single job IO
- page copy: 2.54M vs. 2.6M(BATCH_IO), +2.3%
- zero copy(--auto_zc): 3.13M vs. 3.35M(BATCH_IO), +7%

V4:
- fix handling in case of running out of mshot buffer, request has to
be un-prepared for zero copy
- don't expose unused tag to userspace
- replace fixed buffer with plain user buffer for
UBLK_U_IO_PREP_IO_CMDS and UBLK_U_IO_COMMIT_IO_CMDS
- replace iov iterator with plain copy_from_user() for
ublk_walk_cmd_buf(), code is simplified with performance improvement
- don't touch sqe->len for UBLK_U_IO_PREP_IO_CMDS and
UBLK_U_IO_COMMIT_IO_CMDS(Caleb Sander Mateos)
- use READ_ONCE() for access sqe->addr (Caleb Sander Mateos)
- all kinds of patch style fix(Caleb Sander Mateos)
- inline __kfifo_alloc() (Caleb Sander Mateos)

V3:
- rebase on for-6.19/block
- use blk_mq_end_request_batch() to free requests in batch, only for
page copy
- fix one IO hang issue because of memory barrier order, comments on
the memory barrier pairing
- add NUMA ware kfifo_alloc_node()
- fix one build warning reported by 0-DAY CI
- selftests improvement & fix

V2:
- ublk_config_io_buf() vs. __ublk_fetch() order
- code style clean
- use READ_ONCE() to cache sqe data because sqe copy becomes
conditional recently
- don't use sqe->len for UBLK_U_IO_PREP_IO_CMDS &
UBLK_U_IO_COMMIT_IO_CMDS
- fix one build warning
- fix build_user_data()
- run performance analysis, and find one bug in
io_uring_cmd_buffer_select(), fix is posted already

Ming Lei (27):
kfifo: add kfifo_alloc_node() helper for NUMA awareness
ublk: add parameter `struct io_uring_cmd *` to
ublk_prep_auto_buf_reg()
ublk: add `union ublk_io_buf` with improved naming
ublk: refactor auto buffer register in ublk_dispatch_req()
ublk: pass const pointer to ublk_queue_is_zoned()
ublk: add helper of __ublk_fetch()
ublk: define ublk_ch_batch_io_fops for the coming feature F_BATCH_IO
ublk: prepare for not tracking task context for command batch
ublk: add new batch command UBLK_U_IO_PREP_IO_CMDS &
UBLK_U_IO_COMMIT_IO_CMDS
ublk: handle UBLK_U_IO_PREP_IO_CMDS
ublk: handle UBLK_U_IO_COMMIT_IO_CMDS
ublk: add io events fifo structure
ublk: add batch I/O dispatch infrastructure
ublk: add UBLK_U_IO_FETCH_IO_CMDS for batch I/O processing
ublk: abort requests filled in event kfifo
ublk: add new feature UBLK_F_BATCH_IO
ublk: document feature UBLK_F_BATCH_IO
ublk: implement batch request completion via
blk_mq_end_request_batch()
selftests: ublk: fix user_data truncation for tgt_data >= 256
selftests: ublk: replace assert() with ublk_assert()
selftests: ublk: add ublk_io_buf_idx() for returning io buffer index
selftests: ublk: add batch buffer management infrastructure
selftests: ublk: handle UBLK_U_IO_PREP_IO_CMDS
selftests: ublk: handle UBLK_U_IO_COMMIT_IO_CMDS
selftests: ublk: handle UBLK_U_IO_FETCH_IO_CMDS
selftests: ublk: add --batch/-b for enabling F_BATCH_IO
selftests: ublk: support arbitrary threads/queues combination

Documentation/block/ublk.rst | 60 +-
drivers/block/ublk_drv.c | 1312 +++++++++++++++--
include/linux/kfifo.h | 34 +-
include/uapi/linux/ublk_cmd.h | 85 ++
lib/kfifo.c | 8 +-
tools/testing/selftests/ublk/Makefile | 7 +-
tools/testing/selftests/ublk/batch.c | 604 ++++++++
tools/testing/selftests/ublk/common.c | 2 +-
tools/testing/selftests/ublk/file_backed.c | 11 +-
tools/testing/selftests/ublk/kublk.c | 143 +-
tools/testing/selftests/ublk/kublk.h | 195 ++-
tools/testing/selftests/ublk/null.c | 18 +-
tools/testing/selftests/ublk/stripe.c | 17 +-
.../testing/selftests/ublk/test_generic_14.sh | 32 +
.../testing/selftests/ublk/test_generic_15.sh | 30 +
.../testing/selftests/ublk/test_generic_16.sh | 30 +
.../testing/selftests/ublk/test_stress_06.sh | 45 +
.../testing/selftests/ublk/test_stress_07.sh | 44 +
tools/testing/selftests/ublk/utils.h | 64 +
19 files changed, 2563 insertions(+), 178 deletions(-)
create mode 100644 tools/testing/selftests/ublk/batch.c
create mode 100755 tools/testing/selftests/ublk/test_generic_14.sh
create mode 100755 tools/testing/selftests/ublk/test_generic_15.sh
create mode 100755 tools/testing/selftests/ublk/test_generic_16.sh
create mode 100755 tools/testing/selftests/ublk/test_stress_06.sh
create mode 100755 tools/testing/selftests/ublk/test_stress_07.sh

--
2.47.0